Electrical or electronic automatic control units generally comprise one or more inputs for signals, in particular for analog signals provided by sensors of physical parameters such as pressure, temperature, linear displacement or any other type of parameter. The automatic control unit is made so as to carry out functionalities preprogrammed on the basis of the level or of the state of these parameters.
FIG. 1a shows the schematic of a prior art analog input 10 connected to the output of a sensor 12 providing the analog input with a voltage Vs dependent on a physical parameter used by the automatic control unit.
The analog input 10 essentially comprises an analog/digital converter 14 fed, via its analog input 16 through a level adaptation interface 18, with the voltage Vs output by the sensor and a voltage reference Vr 20 for the analog/digital converter 14.
The analog/digital converter 14 provides a digital cue, at its digital output 22, dependent on the level of the input voltage Vs applied to its analog input 16. This digital cue is used by an electronic processing circuit, for example an automatic control unit.
The voltage reference 20 is necessary to obtain the precision of conversion into digital of the analog voltage applied to the input 16 of the analog/digital converter 14.
The theoretical dynamic range of the analog input level Vs is a fixed value corresponding to the normalized standard dynamic range of the sensors, for example from 0 to 10 volts.
FIGS. 1b, 1c and 1d show respectively three types of sensors 24, 26 and 28 that can be connected to the analog input of FIG. 1a. 